The Canadian Tribals were intended to receive a dual 4.5-inch high-angle fit, but the upper-deck mounting did not mature in wartime and ultimately appeared with the Daring class. A 4.7-inch solution would begin from a working open mount already fitted widely, although its gun axis would need to be raised or otherwise rearranged to reach 80 degrees. The gun would return to roughly 50 or 60 degrees for loading rather than being loaded at maximum elevation. Existing C- and D-class cruiser conversions likewise make the earlier upper-deck option operationally significant.
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Why the 4.5-inch upper-deck mount arrived too late
The alternate 4.7-inch programme gains its timing advantage from modifying an existing upper-deck mount rather than waiting for the delayed 4.5-inch destroyer installation.